Sulfur fate during bituminous coal combustion in an oxy-fired circulating fluidized bed combustor

To clarify the sulfur transformation behavior during oxy-fired circulating fluidized bed (CFB) combustion, experiments on SO2 emission characteristics were carried out in a 50 kWth CFB combustor. Results show that SO2 emission is quite dependent on the bed temperature in different atmospheres without limestone injection. With Ca/S=2.5, SO2 emission in 21%O2/79%CO2 atmosphere is smaller than that in air atmosphere, but SO2 emission decreases with the increase of O2 concentration. The calcium forms in the ash prove the combination of calcination/carbonation and direct sulfation mechanism of limestone under oxy-combustion conditions. And the desulfurization efficiency of limestone (as deducting the self-retention efficiency from the total sulfur removal efficiency) increases from 40% to 52% as the O2 concentration increases from 21% to 40%.